Upcoming improvements to pip 1.4 (wheel support and
skip-pre-release-by-default) mean that pytz without a version
will be skipped. Adding a version here gets us what we want.
Adding an intial lower-bound on the version that's currently in RHEL6,
since we don't actually care about the version itself.
pytz uses date based versioning which isn't supported by default:
http://www.python.org/dev/peps/pep-0440/#date-based-versions
Change-Id: Ieb0cda61b2f8665d5f83ff8beb8a4cf5b4ece011